Yoko Nishi

Heavy oil sorption and recovery by using carbon fiber felts

On fibrous carbon materials, including activated carbon fibers, sorption capacity for heavy oils, less viscous A-grade and more viscous C-grade, was determined. Sorption capacity depended strongly on their bulk density; the correlation was the same as that found previously on exfoliated graphite and carbonized fir fibers. On carbon fiber felts, excellent recycling performance was observed, though sorption capacity was not so high as on exfoliated graphite and carbonized fir fibers. By filtration under suction, about 90% of sorbed A-grade heavy oil could be recovered and no decrease in sorption capacity was detected even after eight cycles. By washing with solvents, n-hexane for A- and C-grade oils and A-grade oil for C-grade oil, almost 100% recovery with no marked reduction in sorption capacity was found for each cycle. For the felts of PAN-based carbon fibers, rather severe operations for oil recovery, centrifugation and squeezing with twisting, could be applied without pronounced decreases in sorption capacity and recovery ratio.

SORPTION KINETICS OF HEAVY OIL INTO POROUS CARBONS

Sorption kinetics of heavy oil into porous carbons was evaluated by a concept of liquid sorption coefficient obtained from the weight increase of heavy oil with sorption time, which was measured by a wicking test. Exfoliated graphite, carbonized fir fibers and carbon fiber felts were used as porous materials. It was found that the liquid sorption coefficient of fibrous carbons was twice larger than that of exfoliated graphite. Such a difference in the liquid sorption coefficient between the exfoliated graphite and two fibrous carbons was caused by a difference in effective sorption porosity and tortuosity between them. For the exfoliated graphite and carbonized fir fibers, the liquid sorption coefficient and the effective sorption porosity were strongly dependent on their density. The maximum values of both liquid sorption coefficient and effective sorption porosity of the exfoliated graphite were shown at the bulk density around 16 kg/m3. The liquid sorption coefficient of the carbonized fir fibers increased with increasing the density in the range from 6 to 30 kg/m3. When the carbonized fir fibers were densified above 30 kg/m3, the sorption rate was saturated. On the other hand, the sorption kinetics into the carbon fiber felt was almost independent of the bulk density, because the density of the carbon fiber felt is not effective for the pore structure. The effect of bulk density on the sorption kinetics could be supported from an analysis of pore structure of the porous carbons with different densities, which was measured by mercury porosimeter.

Sorption and recovery of heavy oils using exfoliated graphite. Part IV: Discussion of high oil sorption of exfoliated graphite

Abstract The correlation between sorption capacity for heavy oil with a viscosity of 0.004 kg/m s and pore volume measured by a mercury porosimeter was studied on exfoliated graphite samples with different bulk densities. Pore volume measured by using the conventional dilatometer (N-type cell), which gives information on the pore size from 0.004 to 4 μm, was too low to explain the sorption capacity measured. However, pore volume measured by a special dilatometer (U-type cell) for large pore sizes up to 600 μm was very closed to sorption capacity. Pore volume measured by this U-type cell showed a linear relation to sorption capacity of exfoliated graphite samples, of which the slope was the same value as the density of heavy oil used (860 kg/m 3 ). Therefore, large pores, which are reasonably assumed to be inter-particle pores among entangled worm-like particles of exfoliated graphite, were responsible for the large sorption capacity of heavy oils. Intra-particle pores inside and cleavage-like pores on the surface of worm-like particles were assumed to assist the capillary pumping of heavy oil.

Preparation of microporous carbon foams for adsorption/desorption of water vapor in ambient air

Microporous carbon foams were prepared from a fluorinated polyimide using melamine foam as a template. The adsorption/desorption behavior of water vapor in ambient air was examined. The activation of carbon foams at 400℃ for 1h in air was found to be effective in increasing the adsorptivity of water vapor. The amount of water vapor adsorbed after air activation was almost 3 times as large as that before activation, although the micropore volume increase was only 1.5 times. The reversible adsorptivity for water vapor in ambient air showed a linear dependence on micropore volume with an adsorptivity of about 40% mass fraction for a micropore volume of 0.75mL/g.

NO reduction over ultrafine metal-tailored microporous carbon at ambient temperature

In a previous letter we reported NO is rapidly reduced to N 2 over an ultrafine Ru-particle-dispersed activated carbon fiber (ACF) at an ambient temperature. This paper described that Pt, Cu or Fe-tailored ACF can induce a similar NO reduction at an ambient temperature.

Water Vapour Adsorption of Microporous Carbon Films Prepared from Fluorinated Aromatic Polyimides

The adsorption of water vapour onto microporous carbon films derived from fluorinated aromatic polyimides was studied at 25°C over the relative pressure range 0–0.95. The carbon films prepared were microporous with a high micropore volume ranging up to 0.44 ml/g and a sharp pore-width distribution at ca. 0.6 nm. The adsorption/desorption isotherm of water vapour onto the carbon films was of type V with slight hysteresis. The carbon films derived from fluorinated polyimides were found to exhibit a much higher water vapour adsorption at low relative pressure regions relative to commercially available activated carbon fibres, with their saturated adsorption capacities being dependent on their micropore volumes. The microporous carbon derived from the polyimide with the highest fluorine content (31.3 mass%) showed the highest saturated adsorption capacity of ca. 465 mg/g, with 90 mass% of the water vapour being adsorbed at a relative pressure below 0.46. Both the high micropore volume and the high water vapour adsorption were maintained even after heat treatment at 1300°C, although the steep uptake of water vapour was shifted to higher relative pressures to some extent.

Gas Adsorption/Desorption Isotherm for Pore Structure Characterization

Abstract The measurement and analysis of gas adsorption/desorption isotherms are explained for the characterization of pore structure of carbon materials. Practical key issues for the measurements of isotherms and the analysis by different methods are summarized. Some experimental results on microporous and mesoporous carbons are presented. The analyzed data obtained by the instrument does not guarantee the appropriateness of the analysis method applied on the sample, although most instruments provide the analysis data automatically. It is strongly recommended to confirm whether the fundamental relations giving the pore parameters are satisfying the theory of the analyzing method.